1. Field of the Invention
This invention relates to a borosilicate glass with a special absorption edge, and to uses for the borosilicate glass.
2. Discussion of Related Art
In order to filter, in a targeted manner, a UV range which generally is defined as below 400 nm and can be divided into three sub-ranges, UVA, UVB and UVC, so-called colorless glasses or also optical glasses with defined absorption edges are used. The absorption edge or edge wavelength λc corresponds to half of the pure transmission maximum value between the blocking and permeable range.
A spectacle glass is known from European Patent Reference EP 0 151 346 B1 which has a UV edge in the range between 325 nm and 335 nm. TiO2 is added to the glass for this purpose. The proportion of TiO2 is thus 4–6% by weight on an oxide basis.
This type of glass is not suitable for commercial application cases, in which a dimensional stability even at high glass transformation temperatures, for example >560° C., and/or a stable thermal expansion coefficient is required.
A stable expansion coefficient facilitates the incorporation or respectively exchange of the glasses in components.
Another important aspect for the glasses in such technical applications is their transmission course including the UV edge. A defined steep UV edge is required in the UV range corresponding to the application purpose. For example, for illumination tables for burning-in phosphorus units into television screen units, UV radiation of >320 nm is required. For experiments with plants in plant cultivation, hard UV radiation of >280 nm is also definitely used. Weathering instruments for quality control change the UV ranges, and thus filters according to each requirement.
Japanese Patent Reference JP 52-66512 A describes UV filter glass with an absorption edge of approximately 370 nm made of a borosilicate glass which necessarily contains CeO2 and otherwise in combination with TiO2. The CeO2 significantly increases the material costs in the glass. In addition, CeO2 has a negative effect on the solarization of the glass.
German Patent Reference DE 639 456 A1 describes a lamp glass, made of a glass with a relatively wide composition range, in which SiO2, B2O3 are components and Al2O3, MgO, CaO, BaO, BeO, Na2O and K2O can be contained. The glass has no defined UV edge or optical situations.
United Kingdom Patent Reference GB 20 02 341 describes an optical fibre glass with a relatively wide composition range, in which SiO2, B2O3 are components and Al2O3, MgO, CaO, BaO, SrO, Na2O and K2O can be contained. The glass has no defined UV edge, but rather glasses/fibres with refraction index gradients.
U.S. Pat. No. 2,832,491 corresponds to a method patent, which is suitable for pre-loading of glass panes. The composition of the glass which is suitable for pre-loading contains in turn SiO2 and B2O3 as components in a relatively wide range. Exact UV edges and optical situations cannot be set with this glass.
German Patent Reference DE 195 32 800 A1 comprises the use of glasses for disinfection. A high transmission in the UVB and UVC range with reduced transmission in the visible and IR range is ensured by these glasses. Consequently, glasses with high transmission in the pass range are not possible.
German Patent Reference DE 38 22 733 A1 describes solder glass made of a glass with a relatively wide composition range, in which SiO2, B2O3 are components and Al2O3, MgO, CaO, BaO, SrO, ZnO, Li2O, Na2O and K2O can be contained, containing at most 1% by weight alkaline earth metal oxides. An alkaline earth content of at least 1% by weight ensures a good chemical resistance, which permits the application of these filter glasses in a humid climate. The glass taught by German Patent Reference DE 38 22 733 A1 does not make it possible to set a defined UV absorption edge.
European Patent Reference EP 0 505 061 A1 describes glass for protection covers for gallium arsenide solar cells with high UV absorption in the wavelength range of less than 320 nm. It contains SiO2, B2O3, Na2O, K2O and CeO2 as components. Al2O3, TiO2, MgO, CaO, ZnO, SrO, BaO, PbO, Li2O, As2O3, Sb2O3 and F are optionally contained. High UV transmissions are specifically avoided in the case of the described glasses.
European Patent Reference EP 0 953 549 A1 describes glass for glass plates and substrates, which are used in electronics. The physical properties, such as expansion coefficient, the lower strain point, the density and the oxygen atom density are essential here. However, the UV absorption edge or the optical properties are not relevant for these glasses.